Styrene is typically produced commercially by dehydrogenating ethylbenzene in the presence of an iron-based catalyst. This reaction is endothermic and equilibrium limited. The process is usually operated at temperatures between about 600-850° C. and at atmospheric or sub-atmospheric pressure. Steam is often co-fed to the reactor with the ethylbenzene. A problem with the process is that it consumes a high level of energy. The conversion of ethylbenzene is typically below 65% to maintain selectivity to styrene in excess of 95%. As a result, reactant recycles are often needed. However, the separation of unreacted ethylbenzene from styrene is costly due to the close boiling points of ethylbenzene (136° C.) and styrene (145° C.).
The use of oxidative dehydrogenation of ethylbenzene has been suggested as a substitute for the dehydrogenation of ethylbenzene. Thus far this process has not been commercialized. This reaction is exothermic. Although high styrene selectivities may be achieved, ethylbenzene conversions less than 60% are typically obtained in order to provide for such high selectivities. An increase in the reaction temperature may increase the ethylbenzene conversion, but styrene selectivity tends to decrease significantly due to combustion of styrene and ethylbenzene. The presence of hot spots in the catalyst bed tends to sinter the catalyst resulting in catalyst deactivation.
This invention, in at least one embodiment, provides a solution to these problems.